The present invention relates to a process for hydrogenating olefinic unsaturated groups by contacting a solution of polymers containing the olefinic unsaturated groups with hydrogen in the presence of a hydrogenation catalyst. More specifically, the present invention relates to a process for hydrogenating a polymer wherein at least one part of a hydrogenated polymer solution is recycled and hydrogenated in the above-mentioned process.
A polymer containing olefinic unsaturated groups has disadvantages of being inferior in stability, such as heat resistance and oxidation resistance due to olefinic unsaturated groups, while the olefinic unsaturated groups are advantageously used for the vulcanization or the like. These disadvantages are remarkably improved by hydrogenating olefinic unsaturated groups in polymer chains.
The present applicant has already taught hydrogenation processes using metallocene type catalysts in Japanese Patent Application Laid-Open Nos. 61-28507, 61-33132, 61-47706 and 62-209103, Japanese Patent Publication Nos. 63-5402 and 1-53851, and the like. These inventions relate to a batch hydrogenation process. However, metallocene type catalysts are not only expensive but also have disadvantages of being easily inactivated by the rise of temperature caused by the heat of the hydrogenation reaction or the like. Owing to these disadvantages, the catalysts have been used in an amount more than necessary or hydrogenation reaction periods have become long. As a result, problems in production costs have been caused.
On the other hand, Japanese Patent Application Laid-Open No. 8-109219 discloses a production process of a hydrogenated polymer having an excellent weather resistance wherein a polymer solution containing olefinic unsaturated groups, hydrogen gas, and a hydrogenation catalyst are continuously supplied to a tank reactor equipped with a stirrer and the reaction product is continuously taken out. Japanese Patent Application Laid-Open No. 11-286513 discloses a continuous production process of a hydrogenated polymer containing olefinic unsaturated groups wherein plural reactors are connected in series and hydrogen is supplied to at least one of the reactors from the lower portion thereof.
However, according to these processes, it has been difficult to maintain and control a desirable degree of hydrogenation in the case of a long-term continuous operation. Particularly, in the case of production of a highly hydrogenated polymer, a polymer having a lower degree of hydrogenation than aimed has been disadvantageously obtained, or the hydrogenation reaction has had to be restarted after the continuous hydrogenation reaction is once stopped to adjust the hydrogenation condition when the hydrogenation reaction is not performed properly. Additionally, in the case of these continuous hydrogenation processes, the amount of catalysts used have disadvantageously increased though productivity has been higher than a batch hydrogenation process.
Therefore, it has been strongly desired to develop methods for overcoming these problems.
An object of the present invention is to provide a process for hydrogenating a polymer containing an olefinic unsaturated group which can steadily maintain or control a desirable degree of hydrogenation for a long term.
The present inventors have studied the above-mentioned problems extensively and intensively. As a result, the inventors have found that the above-mentioned problems can be solved by recycling one part of a hydrogenated polymer solution to the reactor, and thus accomplished the present invention.
Namely, the present invention is:
(1) A process for hydrogenating a polymer, which process comprises the steps of:
contacting a polymer solution containing an olefinic unsaturated group with hydrogen in the presence of a hydrogenation catalyst to hydrogenate the olefinic unsaturated group of the polymer; and
recycling at least one part of the resultant hydrogenated polymer solution for hydrogenation.
The present invention also covers the following preferred embodiments.
(2) The process according to the above-mentioned process (1), wherein the polymer solution containing an olefinic unsaturated group is continuously supplied to a reactor to continuously hydrogenate the olefinic unsaturated group of the polymer, and the resultant hydrogenated polymer solution is continuously taken out from the reactor and then one part thereof is continuously recycled to the reactor for hydrogenation.
(3) The process according to the above-mentioned process (2), wherein the hydrogen is supplied from near the bottom of the reactor.
(4) The process according to the above-mentioned process (2) or (3), wherein the reactor is a tank reactor, the polymer solution containing an olefinic unsaturated group is supplied from near the top of the reactor, and the resultant hydrogenated polymer solution is taken out from near the bottom of the reactor or a piping arranged out of the reactor to recycle one part thereof to the reactor for hydrogenation.
(5) The process according to any one of the above-mentioned processes (2) through (4), wherein the reactor is a tank reactor having an L/D of from 1 to 8 and being equipped with a stirrer, wherein L represents a length between an upper tangent line and a lower tangent line of the reactor and D represents an inner diameter of the reactor.
(6) The process according to the above-mentioned process (2) or (3), wherein the reactor is a column or tube reactor, the polymer solution containing an olefinic unsaturated group is supplied from near the bottom of the reactor, and one part of the polymer solution hydrogenated in the reactor is continuously taken out from near the top of the reactor or a piping arranged out of the reactor to recycle one part thereof to the reactor.
(7) The process according to any one of the above-mentioned processes (1) through (6), wherein the hydrogenation catalyst is supplied two or more times to conduct hydrogenation.
(8) The process according to the above-mentioned process (1), wherein a reactor group comprising two or more reactors connected in series is used, the polymer solution containing an olefinic unsaturated group is continuously supplied to the first reactor of the reactor group, the hydrogen is supplied to at least one reactor of the reactor group to continuously hydrogenate the olefinic unsaturated group of the polymer, and the resultant polymer solution hydrogenated in at least one reactor of the reactor group is continuously taken out to continuously recycle one part thereof to the reactor and/or a reactor arranged upstream of the reactor for hydrogenation.
(9) The process according to the above-mentioned process (8), wherein the hydrogen is supplied from near the bottom of at least one reactor of the reactor group.
(10) The process according to the above-mentioned process (8) or (9), wherein the first reactor is a tank reactor having an L/D of from 1 to 8 and being equipped with a stirrer, and the second and following reactors arranged downstream of the first reactor are at least one kind selected from the group consisting of a tank reactor having an L/D of from 1 to 8 and being equipped with a stirrer, a column reactor having an L/D of 2 or more and a tube reactor having an L/D of 2 or more.
(11) The process according to any one of the above-mentioned processes (8) through (10), wherein at least one reactor is a tank reactor, the polymer solution containing an olefinic unsaturated group is supplied to the reactor from near the top thereof, and one part of the resultant polymer solution hydrogenated therein is continuously taken out from near the bottom of the reactor or a piping arranged out of the reactor and then is recycled to the reactor or a reactor arranged upstream of the reactor.
(12) The process according to any one of the above-mentioned processes (8) through (10), wherein at least one reactor is a column or tube reactor, the polymer solution containing an olefinic unsaturated group is supplied to the reactor from near the bottom thereof, and one part of the resultant polymer solution hydrogenated in the reactor is continuously taken out from near the top of the reactor or a piping arranged out of the reactor and then is recycled to the reactor or a reactor arranged upstream of the reactor.
(13) The process according to any one of the above-mentioned processes (8) through (12), wherein the hydrogenation catalyst solution is supplied to the first reactor and is additionally supplied to at least one of the reactors arranged downstream of the first reactor.
(14) The process according to any one of the above-mentioned processes (2) through (13), wherein the continuous hydrogenation is initiated after the polymer solution containing an olefinic unsaturated group is hydrogenated to a desirable degree of hydrogenation.
(15) The process according to any one of the above-mentioned processes (1) through (14), wherein the mass ratio between the polymer containing an olefinic unsaturated group to be supplied to the reactor and the resultant hydrogenated polymer to be recycled is from 1/50 to 50/1.
(16) The process according to the above-mentioned process (1), wherein the hydrogenation reaction is a batch type.
(17) The process according to the above-mentioned process (16), wherein the hydrogenation catalyst is supplied two or more times.
(18) The process according to the above-mentioned process (17), wherein timing of the second and following supply of the hydrogenation catalyst is determined by measuring an absorption rate of hydrogen.
(19) The process according to the above-mentioned process (18), wherein timing of the second and following supply of the hydrogenation catalyst is at a time when the absorption rate of hydrogen decreases to 80% or less of an initial absorption rate of hydrogen at the beginning of the hydrogenation reaction.
(20) The process according to the above-mentioned process (17), wherein an amount of the first supply of hydrogenation catalyst is controlled so that a degree of hydrogenation at the time of the second and following supply is from 50% to 90%.
(21) The process according to any one of the above-mentioned processes (1) through (20), wherein the resultant hydrogenated polymer solution is recycled through a heat exchanger.
(22) The process according to any one of the above-mentioned processes (1) through (21), wherein the hydrogenation catalyst is a metallocene compound.